An X-ray tube is mounted on various X-ray inspection apparatuses such as a CT (computed tomography) device. The X-ray tube includes a rotatable anode target for an X-ray tube. The rotatable anode target includes a disc-shaped member including an X-ray irradiator, and a rotation shaft integrated with the disc-shaped member. A rotatable anode target radiates an X-ray by an electron beam emitted from a cathode irradiated on the X-ray irradiator. When the X-ray radiation is repeated, a temperature at the X-ray irradiator increases. The rotatable anode target is easy to be thermally deformed under a high-temperature.
A rotation structure of the rotatable anode target is divided into two kinds of structures of a ball bearing structure using a bearing ball and a dynamic pressure bearing structure. The ball bearing structure is a structure where the rotation shaft is rotated while being supported by the bearing ball. The dynamic pressure bearing structure is a structure including: a cylinder of a rotation shaft having a cylindrical shape; a fixed shaft provided in the cylinder and having a spiral shape or the like; and a sliding bearing having a liquid-metal lubricant such as a liquid metal filled in the cylinder.
The ball bearing structure is a structure including the bearing ball, and therefore, it is possible to obtain a stable high-speed rotation. However, there has been a problem that an operation sound is loud because the rotation shaft is in contact with the bearing ball.
The dynamic pressure bearing structure is a structure including the sliding bearing. Accordingly, the operation sound and vibration are very small. Besides, abrasion is also small, and therefore, operating life thereof is long. The dynamic pressure bearing structure uses the liquid-metal lubricant such as the liquid metal, and therefore, it is excellent in heat release performance at the disc-shaped member including the X-ray irradiator.